The work of Susuma Tonegawa, Nobel Prize for Medicine in 1987, has shown the immunological function of certain cells of the epidermis, the Langerhans cells, with respect to localized aggressions in the epidermal layer of the skin. The Langerhans cells, that belong to a so-called lymphoid dendritic cell family, essentially are located in the middle layers of the epidermis. Despite their low density, their function is one of information and surveillance over the entire epidermis thanks, especially, to their dendritic nature and to their migratory capability.
The Langerhans cells are capable both of ingesting foreign bodies or allergens that have penetrated into the epidermis, and of transmitting antigens to special immuno-competent cells, the so-called T cells. The activation and protection produced by the Langerhans cells thus make it possible to stimulate the process of intrinsic defense of the epidermis.
Now, it is well known that these cells are directly exposed to ultraviolet rays resulting from exposure to the sun. Recent studies have shown that these radiations to a more or less important extent cause, on the one part, a decrease of the membrane markers, that is to say an alteration of the capability of the presentation of antigens to the immunocompetent cells and, on the other part, a disappearance of the dendrites that characterize the Langerhans cells. In case of extended exposure to the sun, the ultraviolet rays inhibit the Langerhans cells and the latter see their number decrease.
It has been sought to prepare products capable of protecting and of activating the Langerhans cells as a precaution against ultraviolet rays that frequently act on the epidermis.
Thus there are known products prepared from yeast membrane extracts, constituted by polysaccharides of vegetable origin. The products obtained, that are members of the .beta.-1,3 glucanes family, are recognized by the membrane receptors of the Langerhans cells, and it enables these cells to maintain to some extent their macrophagic activity and to protect the immunocompetent cells of the epidermis.
A major drawback of the aforementioned products is found in the relatively high cost associated with their preparation process.